Larval Transport by Internal Tidal Bores

8 Biology Department

iology Department research covers a research on how pollution affects marine ticipated fully in an Alvin cruise in May, and Bwide range of organisms from viruses organisms, and acoustical, anatomical, and continued working through much of the and bacteria to algae, zooplankton, whales, behavioral studies of whales and dolphins. summer with his characteristic passion, thor- and birds. We use an equally broad array of In the face of ever tighter Federal sup- oughness, and charm. He received the Bergey methods and approaches, including molecu- port for basic research in biological ocean- Award from the Bergey’s Manual Trust in lar biology; video microscopy and flow ography, our scientists have turned to in- 1998 for long-term distinguished achieve- cytometry; acoustic, video, and net sam- creasingly diverse sources of support and ment in bacterial taxonomy. pling; behavioral observations; and math- new kinds of partnerships. We submitted a We were fortunate to be able to appoint ematical modeling and analysis. total of 100 proposals to all sources, and two new Assistant Scientists in 1998, In 1998 the department had 25 scientific received full or partial funding for 46 per- Andreas Teske, working on bacteria from staff, along with 7 Scientists Emeritus, 2 cent of them, for a total of more than $5 hydrothermal vents, and Ken Halanych, who Oceanographers Emeritus, 15 Postdoctoral million in sponsored research in 1998. applies molecular and classical techniques to Scholars, Fellows, and Investigators, 14 Leadership and participation by our staff in problems of evolution and phylogeny in technical staff, 33 Joint Program students, large national and international programs benthic invertebrates. During 1998, Jesús and 29 other support staff. During the year, remains strong, including Joint Global Pineda was promoted to Associate Scientist the Scientific Staff pursued over 150 sepa- Ocean Flux Study research in the Atlantic and Mark Dennett to Research Specialist. rate research projects, publishing about 69 and Southern Oceans, the International Retired Senior Scientist and former Depart- scientific papers. We continue to show great Ridge Inter-Disciplinary Global Experi- ment Chair Joel Goldman was appointed strength in many subdisciplines such as ments and Larvae at Ridge Vents programs Scientist Emeritus, and George Hampson ecology and physiology of bacteria and for hydrothermal vents, the Ecology and became the Department’s second Oceanog- protozoa, bio-optical studies of phytoplank- Oceanography of Harmful Algal Blooms rapher Emeritus. Senior Scientist David ton, advanced optical and acoustic tech- program, and the US Global Ecosystems Caron was awarded the first Mary Sears niques for zooplankton distribution and Dynamics Northwest Atlantic Program on Chair for Excellence in Oceanography, and behavior, and the ecology, behavior, and Georges Bank, which is headquartered in Research Specialist Carl Wirsen received a development of invertebrate larvae. Other the WHOI Biology Department. WHOI Senior Technical Staff Award for his areas of interest include mathematical analy- The department and the entire commu- work in deep-sea microbiology. sis and computer modeling of life history, nity were saddened by the death in September —Laurence P. Madin, Department Chair population dynamics and physical-biological of Holger Jannasch, a world-renowned pio- interactions, toxicological and molecular neer in deep-sea microbiology. Holger par-

Larval Transport By Internal Tidal Bores Jesús Pineda, Associate Scientist New generations of bottom-dwelling coastal marine animals face Processes affecting the larvae offshore a complication on their way to establishing new colonies. The early Currents, behavior, and substrate processes life stages of such organisms as clams, mussels, shrimp, and barnacles Larval transport during settlement processes Natural enemies and live suspended in the water, drifting at the mercy of ocean currents in physical stresses influencing a “larval phase” that generally lasts a few weeks. At the end of it, the adults larvae must find a suitable habitat where they can grow into adults and complete their life cycles. Because ocean currents disperse the larvae far from their birth- places, they may find themselves several miles offshore in deep water just when they are ready to settle in the shallow coastal water—a Jayne Doucette waste of larvae because they will not survive in this situation. + Abundance – After several weeks suspended in the ocean, the probability of a Processes that influence the population abundance of coastal bottom- larva returning to its birthplace must be minimal, and the abundance dwelling organisms, with a barnacle as example. The number of larvae is of the colonizers at a given site is uncoupled from the living condi- larger than the number of adults, as each adult produces a myriad of larvae. Larvae are often found offshore, and before they can settle suc- tions of the adults. A site with no natural enemies and rich in food cessfully at the coast, several conditions must be fulfilled. In each case, may be vacant because currents do not bring larvae, or, on the other the proportion of larvae moving to the next set of processes is smaller. hand, a sub-optimal habitat with scarce food may contain a large Small changes in the proportion of larvae that pass from one step to the number of organisms if currents bring many larvae. Knowledge of next can produce large population changes.

WHOI • 1998 Annual Report Biology Department 9

ocean currents that return Gooseneck warmer water offshore. A few barnacle larvae the larvae to coastal habi- Crab larvae hours later, in the second tats is therefore key to Moss animal larvae phase, the heavier cold water understanding the mainte- Common recedes offshore, and is nance and dynamics of barnacle larvae replaced by warmer offshore coastal species. Understanding surface water. A front or line in larval transport is also important FRONT the sea parallel to the shoreline for managing fisheries and designing marks the boundary between marine reserves. For example, it cold and warm water and leads would be futile to preserve a coastal warmer water the surface water in the second site that contains many adults if their phase, with several other lines or larvae are all wasted because current slicks following shortly. The circulation at that site carries all the lines are created by currents that Onshore larvae offshore. Doucette Jayne concentrate surface buoyant colder water Much of my research focuses on material, and, in the case of a studying the various biological and Schematic representation front, the line contains a large physical phenomena involved in larval of an internal tidal bore front with concentration of floating debris, transport by internal tidal bores. observed circulation. Larvae of two species of barnacle and crabs accu- surf grass, and several species of When waves traveling at the surface of mulate at the front, but larvae of a moss animal (bryozoan) do not. All larvae. Observations of these the ocean approach the beach, they larvae occur offshore of the front, while most larvae found shoreward of fronts revealed both striking the front belong to the bryozoan and one species of barnacle. “feel the bottom,” break, and produce patterns of circulation, capable a surge of surf running upslope. Internal (subsurface) waves, which of concentrating buoyant material, and frontal accumulation of some are also ubiquitous, but slower and much larger than surface waves, species of larvae but not of others. also break when they shoal, producing internal surf. Rather than With funding from the National Science Foundation and propagating along the air-sea interface, internal waves propagate WHOI’s Rinehart Coastal Research Center, we are pursuing many along the interfaces of layers of water of different temperature and questions related to internal tidal bores. They range from the effects salinity that are found in most oceans. These internal tidal bores or of El Niño on this mechanism to its variability along the shore in breaking internal waves often occur about every 12.4 or 24 hours. sites separated by several tens of miles to the fine mechanics of the Recent observations in California show that when internal tidal process of frontal accumulation (the latter in collaboration with Karl bores occur, parcels of water that may be several miles long and Helfrich of the Physical Oceanography Department) and the reasons extend from the beach to about 2 miles offshore are fully replaced by why only some types of larvae accumulate in the fronts while others offshore waters once or twice a day. This dramatic exchange of water do not. Further study should also elucidate the physical effects and brings larvae of coastal species shoreward and occurs in two phases. ecological consequences of internal tidal bores, a process with pro- First, the large internal tidal bore transports vast masses of colder found yet largely unexplored implications for coastal communities. water found at depth towards the shore, displacing the nearshore For more information, visit http://mathecol.whoi.edu/~pineda/

WHOI • 1998 Annual Report