A team of volunteers organized by Chuck Idelberger and Stan Plizga recently carried out a seine survey for fish and large invertebrates at four of 13 ponds in the new 168 acre Broadmoor Park (a former golf course) in Rotonda West. The goal was to determine how different the ponds were and how healthy they seemed to be based on two seines per pond. Such a rapid “bioblitz” obviously cannot be considered the final word on the ecology of these ponds, but it is a qualitative start in understanding how to maintain and improve their health.
We were quite shocked at how different the four ponds were in terms of fish and invertebrate species and water clarity (an estimate of nutrient levels). There were a total of five species of native fish (mosquitofish, warmouth sunfish, swamp darter, brook silverside, sailfin molly) and three species of exotics (jewelfish, walking catfish, blue tilapia). Of these eight kinds of fish, any pond had only three to five species each. There were two primary kinds of large invertebrates, grass shrimp and water scorpions (not real scorpions but predatory hemipteran bugs with sucking mouthparts); two ponds had none and two had both. One pond had very clear water indicating low nutrient levels, and two had very murky water caused by excessive growth of floating algae.
The presence or absence of each species can indicate effects of water quality, food, predation and competition. For example water scorpions are predators on small invertebrates and fish, breathe air and thus can survive in waters of low oxygen, but cannot tolerate much predation by large fish. They were lacking in pond 7 which had very clear and thus clean water, and numbers of predatory fish (warmouths). Water scorpions were abundant in pond 10 which had very poor water quality and no warmouths.
The pond (# 7) with the clearest/cleanest water had dense shrubs (mainly wax myrtle) around the periphery, whereas the others had minimal shoreline vegetation. This may indicate that this vegetation is reducing the flow of nutrients in surface water runoff.
The grass shrimp were surprising in that they were abundant in pond 9 with low water clarity and a lot of floating algae and thus a lot of potential food, but lacking in pond 7 which had high water clarity and little floating algae. They may have a problem with predation in clear water from the abundant warmouths and/or an issue with food in low nutrient waters.
The brook silverside was found only in pond 7 which had the best water clarity/quality. Yet the swamp darter was found only in pond 9 which had low water quality but many potential prey items. The exotic jewelfish was found in all four ponds but was most numerous in ponds 3 and 10 with relatively low water clarity/quality. The jewelfish is a small but very aggressive predator and in the two ponds where it was abundant, there were only two native fish species present. The blue tilapia was not captured in the seines but large fish and their nests excavated in the edges of ponds could be seen in the clearest pond # 7. Tilapia are primarily herbivorous as adults and might compete with large mouth bass for nesting areas and with some birds (especially coots and FL gallinules/moorhens) for food.
So we were astonished how different these adjacent four ponds were and how they seem to illustrate the interactions of physico-chemical (oxygen, nutrients) and ecological (competition for food and space, predation) factors to determine what species of fish and invertebrates are present. Nature is the best teacher and we have at Broadmoor an amazing natural schoolhouse to learn how ponds operate. We look forward to further study of the ponds to learn more about their water chemistry and biota to facilitate development of a management plan.